Pulp Production and Optimization from Cotton Stalks

Abstract

Currently there is no pulp producing factory in Ethiopia. This is because pulp production is highly energy and water intensive, acquiring the raw material (wood cultivation and preparation) is costly and time taking. The study initiated by these problems and aimed at optimizing pulping variables and selecting suitable delignification conditions for the production of pulp from cotton stalk. The influence of operational variables on the pulp yield and lignin dissolution of cotton stalks was studied. Cotton stalks chips were delignified in a laboratory pulp wood according to the Kraft pulping process. The conditions used were: active alkali charge (5- 25%), sulfidity (10-50%), cooking temperature (155-175 oC and cooking time (30 – 150 minutes). The cotton stalks chip size and liquor to solid ratio was kept constant at 2 cm X 0.5 cm X 0.5 cm on average and 5 L to 1 kg, respectively. Experimental data were fitted into a central composite design and a quadratic equation has developed. Model prediction for pulp yield and kappa number showed good agreement with experimental data with error values less than 5%. Optimum pulp percent yield (39.6%) was obtained using at 15% of active alkali, 20% of sulfidity, 165 oC temperature and 30 minutes of cooking time. The study showed that pulping at low temperatures for a short cooking time with high concentration of pulping liquor gives the best compromise for both pulp yield and kappa number/residual lignin content. The result of morphology analysis showed that cotton stalks has similar fiber dimensions with eucalyptus. From the results of the study it is recommended that cotton stalk, which is by product of cotton production, can be used as a raw material for pulp production.